Soft-shell clams (Mya arenaria) are molluscs which are indigenous to coastal New England. Soft-shell clams may develop tumors in the haemolymph which have been described as haematopoietic neoplasms (HN). Recent studies from our laboratory have shown that the prevalence of HN disease ranges form 8% - 27% when clams are collected from tidal flats with no or low-level pollution. However, the prevalence of HN disease sharply rises to as high as 90% when clams are collected from one site in New Bedford Harbor, a site contaminated with extremely high levels of PCB's and heavy metals in the sediments. The goals of the research to be carried out during this 4 year grant period are as follows: 1. to determine by immunochemical methods what cell surface proteins are identified by monoclonal antibodies specific for HN cells. 2. to determine by cell separation techniques if a subset of haemocytes is transformed as evaluated techniques if a subset of haemocytes is transformed as evaluated by EM and MAB studies. 3. to determine, by in vitro manipulation, whether or not retrovirus can be induced. 4. To determine by RFLP and southern-blot analysis using defined probes if retroviral sequences can be detected in HN cells. 5. to determine by light and electron microscopy if monoclonal antibodies cross react with certain tissues. Methods to be used include fluorescence activated cell sorter analyses, the generation, characterization and purification of monoclonal antibodies, in vitro culture of molluscan cells (potential) isolation of virus, SDS-polyacrylamide gels, histopathology, transblotting transmission and scanning electron microscopy, RFLP generation and southern blot analysis.